A means for achieving a controlled drug administration is the use of particulate vehicles with a particle size in the micrometer range or in the nanometer range. The drug is incorporated into the vehicle, examples are O/W emulsions, liposomes, polymer microparticles, polymer nanoparticles, solid lipid nanoparticles, drug microparticles and drug nanoparticles (nanocrystals, nanosuspensions) (R. H. Mxc3xcller, G. E. Hildebrand, Pharmazeutische Technologie: Moderne Arzneiformen, Wissenschaftliche Verlagsgesellschaft Stuttgart). The main purpose of using particulate vehicle systems is, in addition to the reduction of side effects, the establishment of an optimized drug release profile. As a rule, a sustained or at least a prolonged release is sought. High initial release (so-called burst release) is undesired. A standard example of this are polymer microparticles with LHRH analogues for the therapy of prostate carcinoma with a release period over four weeks (commercial products: Decapeptyl, Enantone).
A serious problem which in many cases cannot be solved is a high initial release occurring upon the incorporation of drugs into these drug vehicles. As a rule, emulsions are not suitable for a prolonged release as the active ingredient dissolved in the emulsion drops redistributes itself upon dilution (e.g. injection into the blood) within milliseconds into the aqueous blood phase (C. Washington, in (R. H. Mxc3xcller, S. Benita, B. Bxc3x6hm, Eds.) Emulsions and Nanosuspensions for the Formulation of Poorly Soluble Drugs, medpharm scientific publishers Stuttgart, 101-117, 1998). A prolonged release from liposomes is possible only to a limited extent as identical redistribution processes of the active ingredient and the metabolization of the phospholipids of the liposomes limit the release time. Only with a suitable preparation technique is a sufficiently prolonged release obtained with polymer microparticles (e.g. Decapeptyl), with an unsuitable preparation technique such as ASES (Aerosol Solvent Extraction System) (B. W. Mxc3xcller et al., U.S. Pat. No. 5,043,280 (1991)), a very high initial release is obtained. The achievement of a prolonged release is even more difficult in the case of nanoparticles, as the diffusion paths are very short due to the smallness of the particles, and the degradation rate is sometimes very rapid. Drug release takes place instantly due to diffusion, something which was observed both with polymer nanoparticles and with solid lipid nanoparticles (zur Mxc3xchlen, A. et al. Eur. J. Pharm. Biopharm. 1998, 45, 149-155). In particular from poorly soluble drugs, microparticles can be prepared from pure active ingredient with size reduction processes. Due to the low water solubility of the active ingredients (in general associated with a low dissolution rate) in combination with the relatively low particle surface, a slow release process results. Examples are corticoid microparticle suspensions for intramuscular or intraarticular injection. For some application areas however, a longer release time would be desirable. By means of high-energy milling, poorly soluble drugs can be reduced to nanoparticles (nanocrystals, called nanosuspensions in aqueous dispersion) (Mxc3xcller, R. H. et al., Pharm. Ind. 1999, 61, 1 74-78). Due to the greatly enlarged surface, however, dissolution is very rapid with nanocrystals. Intravenously injected nanosuspensions behaved pharmacokinetically like a solution (e.g. cyclosporine) (H. Sucker, in Pharmazeutische Technologie: Moderne Arzneiformen (R. H. Mxc3xcller, G. E. Hildebrandt, Eds.), Wissenschaftliche Verlagsanstalt Stuttgart, 383-391, 1998). However, microparticles with a size in the lower micrometer range and nanoparticles have advantages described in the literature for drug administration. Thus they adhere to the gastro-intestinal membrane after peroral application. As a result, the bioavailability increases, at the same time the variability decreases. Due to the particle fineness, poorly soluble drugs which do not display sufficient bioavailability after oral application can be injected intravenously (R. H. Mxc3xcller, in Pharmazeutische Technologie: Moderne Arzneiformen (R. H. Mxc3xcller, G. E. Hildebrand, Eds.) Wissenschaftliche Verlagsanstalt Stuttgart, 393-400, 1998). Thus a sufficiently high bioavailability is achieved even with poorly soluble drugs. Due to these advantages, it would be desirable to be able to prepare fine particles in which the fast release due to active ingredient diffusion is eliminated or at least minimized.
In the present invention, this is achieved by linking the drug to the matrix material of the particles by covalent bonds, electrostatic interactions, dipole moments, dispersion forces, ion interactions, hydrogen bonds and/or hydrophobic interactions.
Only one of these types of bond can be present, according to some versions according to the invention, or else several of these types of bond can also be present, according to other versions of the invention.
There are thus
a) Versions with covalent bonds,
b) Versions with non-covalent bonds and
c) Versions with a proportion of covalent and a proportion of non-covalent bonds
In particular in the case of the versions with non-covalent bonds in the form of electrostatic interactions, dipole moments, dispersion forces, ion interactions, hydrogen bridges and/or hydrophobic interactions, a proportion of covalent bonding can also be present according to c) above.
Lipids are used as matrix material.
Conjugates from drugs or prodrugs with lipids are already described in the literature, the aim in this case being to increase membrane permeability and thus drug absorption by coupling an active ingredient with a lipophilic component. A prerequisite for a good absorption is however, in addition to membrane permeability, also a sufficiently high solubility in water. It is of no use if such a conjugate is very lipophilic but at the same time is not very water soluble. Due to the low water solubility, in this case, too little drug reaches the membrane. Dissolution rate and water solubility then become the rate-determining step of the absorption. To prevent this, the aim in the case of these lipid-prodrug conjugates was to prepare conjugates with as high a water solubility as possible. In the present invention, exactly the opposite is the case, the water solubility is to be as low as possible in order to minimize an initial release. The drug is to be released by degradation of the conjugate instead of by diffusion, i.e. after chemical cleavage of the conjugate (e.g. by enzymes in the gastro-intestinal tract or in other body fluids such as blood).
In the present invention, not only are stable conjugates produced by covalent bonds, but also the conjugates produced by non-covalent bonding are so stable, despite the absence of covalent bonding forces, that particles can be prepared from them.
Polymer-drug conjugates often have the problem that, as non-physiological components in the organism, they cannot, or can only slowly, be cleaved. Cleavage of the drug from the polymer is however a precondition for release and therapeutic effectiveness. To achieve a better degradation capability in vivo, lipids are therefore used as matrix material in the present invention. Toxicologically there is also the advantage that the lipid part can be metabolized after the cleavage of the conjugate. It serves at the same time as a nutrient.
In the case of lipid-prodrugs which still have corresponding water solubility, the degradation of the molecule takes place in solution. In the case of the insoluble particles described in this invention, it was found that the lipid conjugate, despite its solid aggregate state, can be degraded. This takes place by the anchoring of enzyme complexes on the particle surface, a surface degradation takes place in which the drug molecules are released (e.g. adsorption of the lipase/colipase complex in the gastro-intestinal tract). The better degradability of lipid-drug conjugates compared with polymer-drug conjugates can be explained in that e.g. the lipid-catabolizing enzymes in the organism are sometimes very unspecifically due to the chemical diversity of the lipids in food. Therefore, lipid-drug conjugates can also be processed accordingly. On the other hand, polymers such as e.g. polymethacrylates and polyhydroxybutyrates (PHBs) do not form part of the human diet. Although PHB is the energy-storage polymer of bacteria, it cannot be degraded by humans in vivo.
The particle matrix of the drug vehicles according to the invention is 100% composed of lipid-drug conjugate (LDC) (Example 1).
The preparation of LDC particles with covalent bonding is carried out e.g. by dispersion or precipitation, generally known methods described in pharmacy and process engineering textbooks being used. Upon dispersion, coarsly dispersed lipids are reduced by mechanical processes. The lipids can be in solid aggregate state (e.g. mortar mill) or in liquid aggregate state (e.g. emulsification of melted lipids by mixers). For the preparation of the LDC dispersion, the lipids can first be reduced and then dispersed in the external (e.g. aqueous) phase or alternatively reduced directly in the external phase. To produce superfine particles in the size range 1-10 xcexcm and in particular in the nanometer range ( less than 1000 nm), high pressure homogenization processes (piston-gap homogenizers, jet stream high pressure homogenizers such as e.g. Microfluidizer) and rotor-stator colloid mills are particularly suitable, the coarsly dispersed matrix material being dispersed in a liquid (e.g. water, non-aqueous media such as polyethylene glycol 400/600 and oils such as Miglyols). In liquid dispersion, the drug vehicles are physically stabilized by surfactants or polymers. No stabilizers are required in dispersion media with sufficiently high viscosity (surfactant-free dispersions). The drug vehicles according to the invention can also be present in a solid dispersion, i.e. the drug carriers are incorporated in a solid external phase, e.g. polyethylene glycol 10000.
Instead of consisting completely of lipid-drug conjugate (LDC), the matrix of the drug vehicles according to the invention can also have a lipid added to it, i.e. consist of a mixture of LDC with one or more lipids (i.e. the matrix is a blend). An example is the mixing of the LDC behenyl alcohol butyric acid ester with cetyl palmitate (example 2) or of the LDC tributyrin with compritol (triglyceride of behenic acid) (example 3). This is recommended in particular when a faster drug release is desirable and the degradation of the LDC is to be accelerated. The addition of a rapidly degradable lipid such as cetyl palmitate leads after its degradation to the enlargement of the surface and resultant rapid degradation of the LDC particles and subsequent drug release.
The preparation of a lipid conjugate with non-covalent bonds is carried out e.g. by melting of the conjugate-forming components (melting method) or by dissolving the components in a common solvent and then evaporating the solvent (dissolution method). Active ingredient and conjugate-forming lipid component are characterized in that that the molecules contain oppositely charged groups (e.g. quaternary ammonium group and dissociated carboxy group) or molecule parts which develop non-covalent interactions with each other (e.g. hydrophobic interactions). Examples of drugs with a primary amino or guanidine function are diminazene, trybizin hydrochloride (SISPI), pentamidine, melarsoprol, cisplatin and hydroxyurea.
Thus, e.g. in the melting method, active ingredient and oppositely charged second conjugate component (e.g. diminazene and stearic acid in the molar ratio 1:2, example 5) are mixed and heated, then cooled, and the conjugate has formed.
In the dissolution method, both components are dissolved in an aqueous or non-aqueous solvent (e.g. diminazene and stearic acid, molar ratio 1:2 in ethanol, example 6) and heated. After evaporation of the ethanol, the conjugate is obtained as residue. There can be used as solvents e.g. water, alcohols, oils, liquid polyethylene glycols (PEGs) or components liquefied by heating (e.g. PEGs or lipids such as Imwitor 900 solid at room temperature) and their mixtures.
A variety of different lipids can be used for the preparation of LDC dispersions. These are both chemically uniform lipids and their mixtures. The lipids are characterized in that they are present in the final product LDC dispersion in the crystalline state (e.g. xcex2-, xcex2i-modification) or in the liquid-crystalline state (xcex1-modification) or in a mixture thereof. When lipid mixtures are used, liquid lipids (e.g. oils, lipophilic hydrocarbons, lipophilic organic liquids such as oleic alcohol) can also be added to the solid lipids (e.g. glycerides, lipophilic hydrocarbons such as hard paraffin) (so-called xe2x80x9clipid blendsxe2x80x9d).
For example, the following lipids are used as dispersed phase and can be applied as individual component or as mixture: Natural or synthetic triglycerides or mixtures of same, monoglycerides and diglycerides, alone or mixtures of same or with e.g. triglycerides, self-emulsifying modified lipids, natural and synthetic waxes, fatty alcohols, including their esters and ethers and in the form of lipid peptides, or any mixtures of same. Particularly suitable are synthetic monoglycerides, diglycerides and triglycerides as individual substances or as mixture (e.g. hard fat), Imwitor 900, triglycerides (e.g. glycerol trilaurate, glycerol myristate, glycerol palmitate, glycerol stearate and glycerol behenate) and waxes such as e.g. cetyl palmitate and white wax (DAB; German Pharmacopeia).
To stabilize the LDC dispersions or modify their surface in a controlled way, surfactants, stabilizers and polymers can be used which are generally known from the preparation of dispersions. Examples of these are:
1. sterically stabilizing substances such as poloxamers and poloxamines (polyoxyethylene-polyoxypropylene block copolymers), ethoxylated sorbitan fatty acid esters, in particular polysorbates (e.g. Polysorbate 80 or Tween 80(copyright)), ethoxylated mono- and diglycerides, ethoxylated lipids, ethoxylated fatty alcohols or fatty acids, and esters and ethers of sugars or of sugar alcohols with fatty acids or fatty alcohols (e.g. saccharose monostearate);
2. charged ionic stabilizers such as diacetyl phosphates, phosphatidylglycerol, lecithins of various origins (e.g. egg lecithin or soya lecithin), chemically modified lecithins (e.g. hydrogenated lecithins), as well as phospholipids and sphingolipids, mixture of lecithins with phospholipids, sterols (e.g. cholesterol and cholesterol derivatives as well as stigmasterol) and likewise saturated and unsaturated fatty acids, sodium cholate, sodium glycocholate, sodium taurocholate, sodium deoxycholate or their mixtures, amino acids or anti-flocculants such as e.g. sodium citrate, sodium pyrophosphate, sodium sorbate [Lucks, J. S. et al. Int. J. Pharm., 1990, 58, 229-235]. Amphotheric surfactants such as e.g. (3-[(3-cholamidopropyl)-dimethyl-ammonio]-2-hydroxy-1-propane sulphonates) [CHAPSO], (3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulphonates) [CHAPS] and N-dodecyl-N,N-dimethyl-3-ammonio-1propane sulphonate. Cationic surfactants, e.g. benzyldimethylhexadecylammonium chloride, methylbenzethonium chloride, benzalkonium chloride, cetylpyridinium chloride.
3. Viscosity increasing substances such as e.g. cellulose ethers and cellulose esters (e.g. methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, sodium carboxy methyl cellulose), polyvinyl derivatives as well as polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate, alginates, polyacrylates (e.g. carbopol), xanthanes and pectins.
The charged stabilizers are, if necessary or desired, preferably contained at the concentration of 0.01% to 20% (m/m) and in particular in a concentration of 0.05% to 10% in the LDC dispersion. Viscosity increasing substances are, if necessary or desired, incorporated in the formulation in a similar ratio, preferably in a quantity of 0.01-20% and in particular in a quantity of 0.1% to 10% (m/m) and preferably in the range between 0.5% and 5%.
There can be used as external phase (dispersion medium, continuous phase) water, aqueous solutions or liquids miscible with water, and glycerine or polyethylene glycol and oily liquids such as Miglyols (medium chain triglyceridesxe2x80x94MCTs) and other oils (castor, peanut, soya, cottonseed, rape seed, linseed, olive, sunflower, saflor oil).
Surfactant-free LDCs are prepared by dispersion of the lipid phase in an aqueous solution which contains one or more viscosity increasing substances, either alone or in combination with other substances, as well as sugar, sugar alcohols, in particular glucose, mannose, trehalose, mannitol, sorbitol as well as others. Furthermore, it is possible to use a combination of the viscosity increasing substances or the combination of same with sugar or sugar alcohols or in a further combination with charge stabilizers or anti-flocculants.
The particle matrix can also consist of a mixture of one or more LDCs and one or more drugs. This can be used in particular when an initial dose is additionally required before a prolonged release.
The particle matrix of the drug vehicles according to the invention can also combine the above the principles, i.e. the matrix consists of a mixture of LDCs, one or more lipids and one or more drugs.
In the LDC particles, the drug can be coupled to various lipids, e.g. one or more diglycerides, monoglycerides, glycerol (e.g. tributyrin), fatty acids, fatty alcohols (e.g. behenyl alcohol-butyric acid ester), functional groups of sterols such as cholesterol and cholesterol derivatives and of waxes.
The bonding of drugs can take place covalently or non-covalently via other interactions (e.g. ion pairs) of various functional groups of the lipid, e.g. hydroxyl groups, carboxy, primary, secondary and quaternary amino groups. In addition to covalent bonding, there can optionally also be a proportion of non-covalent bonding, e.g. ion pairs (vitamin C with lecithin) or conversely, in addition to non-covalent bonding, there can optionally also be a proportion of covalent bonding.
According to the invention, there come into consideration in particular as drugs or drug groups:
butyric acid and in particular behenyl alcohol-butyric acid ester and butyric acid triglyceride (tributyrin), and
xcex2-amino acids and peptides and proteins from these amino acids.
Examples of LDCs with covalent bonding are tributyrin, butyric acid derivatives (e.g. 4-(2-glyceryl)butyric acid, behenyl alcohol-butyric acid ester), retinol palmitate, tocopherol palmitate etc.
Tributyrin is a prodrug of butyric acid which effects cell differentiation in vitro in a large number of neoplastic cells. The clinical use of butyric acid is limited to date due to the difficulties in achieving effective therapeutic concentrations, due to its rapid metabolism [Z. X. Chen et al. Cancer Res. 54 (1994) 3494-3499]. One strategy to achieve effective butyric acid levels in vivo is to use butyric acid compounds as prodrugs which can be metabolized under in vivo conditions to give effective butyric acid concentrations. One of these compounds is tributyrin, 1,2,3 butyric acid glycerol ester, which displayed a high level of biological activity in in vitro trials [Z. X. Chen et al. Cancer Res. 54 (1994) 3494-3499, C. Schrxc3x6der et al. Int. J. Oncol. 13 (1998) 335-1340]. Tributyrin was examined in a phase 1 study as an oral preparation in the treatment of solid tumors. The results were disappointing. No significant tumor regression had taken place. [B. A. Conley et al. Clin. Canc. Res. 4 (1998) 629-634]. This is a result of the rapid metabolism of tributyrin and butyric acid.
Solid lipid drug conjugates (LDCs) have been developed as a new concept of cancer treatment by means of tributyrin, or of the active compound butyric acid. On the one hand tributyrin in mixture with compritol, on the other an ester of behenyl alcohol and butyric acid. The formulation as solid particles opens up the possibility on the one hand of a retarded release of the active ingredient butyric acid, on the other the possibility of the concept of drug targeting, i.e. selective active ingredient application in defined areas. Thus it is possible e.g. to process the LDC particles in a drug formulation for colon delivery and thus to treat local colon carcinoma diseases. Furthermore it is possible to prepare the particles with specific surfactants which make possible a defined accumulation in specific body regions, e.g. Poloxamer 407, accumulation in the bone marrow in the case of leukemia diseases).
When preparing LDC particles by wet-milling of the particle matrix material in melted polyethylene glycol (PEG) 10.000 (e.g. at 80xc2x0 C.), the external phase solidifies upon cooling to room temperature. A solid dispersion is produced, i.e. LDC particles embedded in solid PEG 10.000. This solid dispersion can be processed e.g. milled and processed as powder into tablets and pellets or packed in hard gelatine capsules. For packing in both soft and hard gelatine capsules, the solid dispersion can also be melted again and poured into the capsules in liquid state.
Preparation of dry products from LDC dispersions is possible with customary processing techniques such as e.g. spray-drying, lyophilization, roller drying and vacuum drying. The dry products can then be further processed to traditional drug forms such as e.g. tablets, capsules, pellets, sachets or dry products for reconstitution (e.g. for injectables).